Sewing machines are in widespread use for stitching fabric and such use is intensified in the garment industry where production is a prime consideration. In a common type of stitching operation, the operator of the sewing machine is required to elevate the sewing machine needle to an up position when the stitching operation is complete and the work is to be removed from the machine. At the same time, the operator is frequently required during a stitching operation to maintain the needle in a down position penetrating the work so that the position of the work may be adjusted for another phase of the stitching operation. The common practice in the domestic operation of sewing machines is to simply rotate a hand wheel provided on the sewing machine until the needle occupies the desired position which presents no problem since time and labor are inconsequential factors. However, in the garment industry, having vast numbers of sewing machines and operators, the production rate would be slowed by such a manual operation in addition to imposing a burden on the operator with attendant reduction in efficiency and increased distraction on the part of the operator.
It has therefore been proposed to provide such sewing or stitching machines in an industrial operation with a device for automatically positioning the needle of the machine in a pre selected position during a stitching operation or upon the completion of such a stitching operation. However, such present day devices which are usually of the electrical, electro-mechanical or pneumatic type have been characterized by extreme complexity of construction with resulting high cost and have been difficult to maintain in proper adjustment. Furthermore, such present day needle positioning devices frequently require considerable modification or even incorporation within a sewing machine adding further to the initial cost and maintenance of such sewing machines. In addition, such present day needle positioners generally fail to position the needle at the desired location along its reciprocatory path with the degree of accuracy desired further frustrating the operator.
The following patents are representative of the prior art to which the subject invention pertains all of which disclose arrangements which are clearly distinguishable both structurally and functionally from applicant's invention:
U.S. Pat. No. 3,721,204--Schaffer et al. PA1 U.S. Pat. No. 3,812,801--Lukowicz PA1 U.S. Pat. No. 3,541,982--Marforio PA1 U.S. Pat. No. 3,913,508--Boser PA1 U.S. Pat. No. 3,977,339--Tice
The Tice patent discloses a needle positioner for a stitching machine which utilizes a pneumatically powered positioning motor drivably connected to the sewing machine for moving the needle into a selected position. The Marforio patent relates to a pneumatic drive system for thread cutting devices on a sewing machine which includes a pneumatic drive device and a sensing device for determining whether the sewing machine needle is in its uppermost position. The Schaffer et al. patent teaches an automatic needle positioning device for a sewing machine which utilizes a treadle that controls a needle positioner mechanism so that the needle raises when the treadle is heeled and where the needle always remains down at the end of a stitching operation.
The Lukowicz patent is of general interest relating to a pneumatic drive system for a sewing machine and the Boser patent is directed to a two-needle pneumatic disengaging mechanism for a sewing machine which incorporates a pneumatically actuated needle bar mechanism controlled by a pedal operator remote and pneumatic valves which selectively control the position of either or both needles.